1. Field of the Invention
This invention generally relates to the brewing of beverages. More specifically this invention relates to apparatus for brewing a hot beverage by infusing an infusible material, such as ground coffee, with pressurized liquid, such as water, at an acceptable brewing temperature.
2. Description of Related Art
For many years preparing a beverage, such as coffee, has involved brewing multiple servings in a pot or other container using loose coffee grounds. In some apparatus, the coffee grounds mix with hot water and are then removed from the brewed beverage as, for example, in the so-called “French press” coffee maker. Other apparatus uses a drip brewing procedure that directs hot liquid at low pressure through an open or closed basket containing the loosely ground coffee over a filter, such as a paper filter cone.
The procedures and apparatus for brewing beverages, particularly coffee, have undergone many transformations in recent years spurred by different market requirements. A convenience requirement led to prepackaged packets of ground coffee as a substitute for manually measuring coffee from bulk packages of loose, ground coffee, as in conventional drip coffee makers. A prepackaged packet comprises a permeable filter paper pouch with a pre-measured portion of loose ground coffee. An impervious package stores the packet to maintain freshness. A packet is removed from its package and placed in a basket or like receptacle. Then hot water at atmospheric pressure flows through the packet and its contents for extracting flavor and aroma from the ground coffee.
The foregoing apparatus typically brews multiple beverage servings. Now many users prefer to brew individual servings. This preference for single-serve brewing apparatus, especially for home use, led to the development of pre-packaged disposable capsules, or cartridges, with prepackaged infusible material, and related brewing apparatus. For example, U.S. Pat. No. 4,921,712 (1990) to Malmquist discloses a disposable cartridge for use in an automatic drip-type beverage brewing machine. The cartridge contains a filter member with ground coffee. A closed end of the cartridge has a plurality of holes and forms a shallow receptacle. A user removes a sealing foil from the receptacle and places the cartridge on ledges in a brewing apparatus spaced from a water delivery spout and over the receptacle. The apparatus delivers hot water at atmospheric pressure and at a controlled rate onto the top of the cartridge. Brewed beverage emerges from the bottom of the cartridge for accumulation in the receptacle. There is no requirement for sealing between the apparatus and the cartridge so long as water does not overflow the shallow receptacle.
U.S. Pat. No. 6,612,224 (2003) to Mercier et al. discloses an apparatus for brewing a beverage in which water is fed by gravity from two heated tanks. The temperature of the water in each tank can be adjusted to an optimum value for a different type of brewing. U.S. Pat. No. 6,681,960 (2004) to Garman discloses another low-pressure beverage preparation system in which a brewing chamber receives a cartridge.
Minimizing the brewing time has become another market requirement. It was determined early on that the extraction time or “brewing cycle” of such brewing apparatus could be shortened significantly if the infusible material, such as coffee beans, were ground more finely than those used in such drip-type brewing apparatus. Finer grinding exposes a larger surface area to the water. However, the coffee grounds have a higher packing fraction and volumetric density. This increases hydraulic resistance to the flow of water through the cartridge and the grounds therein. It was found that low pressure apparatus was not efficient for brewing beverages using dense or compacted infusible material.
Rather, water had to be delivered in a closed brewing chamber under an elevated pressure to be able to flow through the coffee in a short period of time. This led to a development of sealed brewing chambers formed by members that are integral to the brewing apparatus. For example, U.S. Pat. No. 4,389,925 (1983) to Paina discloses a beverage extracting and dispensing machine for use with flattened round cartridges. A cartridge contains an infusible product, such as ground coffee, and has permeable upper and lower walls traversing a substantially cylindrical side wall. In this reference a pressure plate coacts with the cartridge to provide sealing.
A myriad of other approaches have been attempted to provide a hot liquid at an elevated pressure for brewing through a cartridge or capsule. For example, U.S. Pat. No. 6,606,938 (2003) to Taylor discloses an apparatus that uses a disposable cartridge that is initially pierced and vented by a tubular outlet probe and then pierced by a tubular inlet probe. Heated liquid is directed into the cartridge through the inlet probe for combination with the beverage medium to produce the beverage. The outlet probe provides a means for extracting the beverage from the cartridge. This apparatus utilizes an air pump and sealed chamber for metering the amount of heated water to be expelled and fed to the cartridge.
U.S. Pat. No. 6,786,134 (2004) to Green discloses a coffee and tea dispenser that infuses material in a cartridge. An injection system, including a water heater and a pump, provides the water under pressure at an elevated temperature.
Similarly, U.S. Pat. No. 7,097,074 (2006) to Halliday discloses a beverage brewing apparatus which includes a cartridge holder held for infusion in the apparatus by a hot liquid under pressure. A water pump and a heater combine to provide hot water at an elevated temperature.
U.S. Patent Application Publication No. US2005/0150391 (2005) to Schifferle discloses a coffee maker in which the coffee is contained in a cartridge. Again, a pump and hot water heater provide water at a brewing temperature to be directed into a brewing chamber including the cartridge.
Any pump configurations for use in brewing apparatus should be able to provide liquid to a brewing chamber at a gauge pressure of about 1 bar (i.e., 1 barg) and at a flow rate in the range of 100 to 400 ml per minute. Reciprocating electromagnetic pumps can satisfy these requirements and are popular for pumping in many beverage brewing apparatuses. U.S. Pat. No. 4,389,169 (1983) to De Dionghi discloses on embodiment that includes a reciprocating piston, a field coil for driving the piston in one direction, a spring for driving the piston in the other direction and suction and delivery valves. As will be apparent and as known, such pumps must be manufactured to close tolerances. Consequently they are expensive components to use in hot beverage brewing apparatus.
The foregoing and other drawbacks have led to the development of brewing apparatus that incorporates a sealed water boiler that heats water above its boiling point. This produces sufficient pressure to drive the liquid from the boiler through the infusible material at an increased pressure. However, at a pressure of 1 barg the boiling point of water increases from 100° C. (the boiling temperature for water at sea level and at standard barometric pressure) to about 120° C. This is well above the acknowledged acceptable brewing temperature range of 90° C. to 96° C. for coffee. As known, brewing a beverage above an acceptable range of brewing temperatures adversely impacts the quality of the brewed beverage. For example, brewed coffee can have a bitter taste and lack any aroma.
U.S. Pat. No. 3,844,206 (1974) to Weber discloses a beverage brewing apparatus with a heating chamber that receives the incoming water. A cover closes the chamber and has pressure regulating and pressure relief valves. The bottom of the heating chamber includes two electric heaters. When the water temperature reaches a proper brewing temperature, the chamber is under a vapor pressure. One of the two heaters is de-energized. Then a valve opens. Water discharges into the infusion chamber under the vapor pressure developed during heating. The infusible material, which is in a cartridge, is also subject to slight increase in pressure so water absorbed in the infusion material is driven from the chamber and into a receptacle.
In the infusion apparatus of U.S. Pat. No. 3,918,355 (1975) to Weber a first chamber contains a liquid, such as water, heated to a predetermined temperature. A second chamber contains the infusion material and is in fluid communication with the first chamber. When the temperature reaches a predetermined value, a latch releases a weight that descends through the first chamber trapping air beneath it. This weight forces hot liquid, under substantially constant pressure, from the first chamber through the passage into the second chamber. Trapped air is then forced through the material to remove any remaining excess liquid.
U.S. Pat. No. 4,147,097 (1979) to Gregg discloses a drip-type coffee maker in which cold water is fed from a reservoir to two heating chambers. One heating chamber is maintained at a temperature that is optimized for interaction with an infusible material. The other chamber maintains water at a higher temperature. The first chamber provides water to the infusible material. The infused liquid discharges into a pot or other receptacle. The second chamber discharges directly into the pot whereby the hot water from the second chamber mixes with the brewed beverage from the brewing chamber to achieve an appropriate drinking temperature.
U.S. Pat. No. 4,287,817 (1981) to Moskowitz et al. discloses another approach in which a conventional heater heats water in a container. The hot water exits from a bottom outlet of the container through valves. Steam can also be produced. Specifically, water in the container is heated to a boiling point that results in the accumulation of steam in the container so the water within the container is forced through an outlet to brew the beverage in an infuser.
Using such brewing apparatus in non-residential environments, such as in hotels or other commercial establishments, imposes still other market requirements. In a hotel environment, for example, in-room coffee apparatus must be compact, inexpensive, reliable and easy to use and must operate with minimal costs. Such brewing apparatus must minimize the efforts of room attendants to clean and maintain the brewing apparatus, to dispose of used coffee grounds and to replenish coffee supplies in the room. In many hotels today in-room coffee apparatus includes a water heater, cups and prepackaged, pre-measured sealed packets of instant coffee. Other hotels have begun to use conventional coffee brewing machines that use capsules or cartridges to brew the coffee.
Notwithstanding the various proposals including those described in the foregoing art, commercially available units for brewing a hot beverage by infusing a material, such as compacted ground coffee, with a hot liquid, such as water, under pressure continue to incorporate both a heater and a pressure pump with the additional costs imposed by the pump and attendant electric and fluid connections and more complex control systems. Such apparatus also tends to be large and bulky. The noise generated by the pump is another deterrent to its use. What is needed is an apparatus for brewing a hot beverage by infusing a material with a hot liquid under pressure at a brewing temperature within the acceptable temperature range, that eliminates the need for a mechanical pump, that reduces manufacturing costs, that maximizes reliability, that is compact and easy for an individual to use and that minimizes the need for regular cleaning and other maintenance.